G’day,
I’m having an issue with the bias-t stopping when i run gr-iridium or multimon-ng in ubuntu 16.04. There is no indication in the command window that it has stopped, but if i give it the off command, i get an access error. When i use any other program (gqrx + decoders, or rtl_433 for example), the bias-t stays active. Thought it might be a blacklist issue, so i have done that. Any ideas please?

What version of the RTL-SDR drivers are you running? Also can I see the exact commands that you are using for gr-iridium and multimon-ng as well?

I think what's happening is that you might be using the latest osmocom drivers. These added bias tee support, but unforunately they reset the bias tee to OFF every time it starts unless the -T flag is specified. So you have to find a way to specify the -T flag to the command line flags if you're using those drivers.

You could also try revert to older drivers, or modify the osmocom driver code to remove the calls to rtlsdr_set_bias_tee.

awesome! -T option works for multimon-ng thanks. the bias-t drivers were installed via the .V3 guide git clone method. would it make any difference if re-install the drivers? is there a correct proceedure to completely remove them?

Unfortunately/fortunately they recently updated their drivers and they now have built in bias tee support. Sounds good, but i've now found that the problem is that in their rtl_fm and other software init code they reset the bias tee to off if no -T flag is specified. So if you turn the bias tee on with our program, then run rtl_fm without the -T flag then the bias tee will reset to off.

For gr-iridium i'm not too sure how that works and how it accesses the RTL-SDR, so not too sure how to fix it. Instead I would first try to install the keenerd version of the drivers from https://github.com/keenerd/rtl-sdr. Use the same instructions but replace the github link with that one. Those drivers dont have the bias tee support built in, so they shouldnt reset the bias tee if you turn it on using our program first.

thanks, yeah, i'm not sure how iridium accsesses the dongle either. there are a set of examples (rules/config) for hackrf, airspy and rtl-sdr within the program so there may be a way to add the bias-t switch there somehow. the hackrf rules show an option for a preamp, so it may be possible. i'm really hoping someone will see this and find a solution, the L-band stuff cant be done without the LNA working.